Panoramic receiver with unwanted signal rejector



R. F. HOLLANDBECK Filed Dec. 50, 1952 PANORAMIC RECEIVER WITH UNWANTED SIGNAL REJECTOR Dec. 13, 1955 'I1-lllI Roymgd F.Ho|londbeck. ATTORNEY United States Patent() PANORAMIC RECEIVER WITH UNWANTED SIGNAL REJECTOR Raymond F. Hollandbeck, Pittsburgh, Pa., assignor to Westinghouse Electric Corporation, East Pittsburgh, Pa., a corporation of Pennsylvania Application December 30, 1952, Serial No. 328,681

6 Claims. (Cl. Z50-20) This invention relates to radio systems, and more particularly to frequency selective control circuits therefor.

It is an object of this invention to provide an improved frequency selective control system.

It is another object to provide an improved frequency selective control system for a frequency sweeping Search receiver that is independent of the strength of the incoming signal.

It is another object to provide an improved frequency selective control system that is capable of varying the sensitivity of a controlled circuit over a predetermined frequency interval which may be automatically shifted in the frequency' spectrum in response to an independent variable.

Still another object of this invention is to provide an improved frequency selective System to vary the sensitivity of the controlled circuit over a frequency interval in which the frequency interval may be easily varied.

These and other objects are effected by my invention as wiil be apparent from the following description and claims taken in accordance with the accompanying drawing throughout which like reference characters indicate like parts and in which:

Figure l is a schematic drawing of a preferred embodiment of my invention, and

Fig. 2 comprises a curve illustrating the response of the frequency selective control system.

Fig. l illustrates a conventional superheterodyne circuit comprising an antenna 3 for receiving incoming signals, a radio frequency amplifier 4, a mixer 19, a plurality of intermediate amplifier stages 5 and 6, a second detector 7 and a final amplifier 8.

Referring in detail to Fig. l, there is shown a sawtooth generator 11 comprising a neon tube 21 with one electrode connected to ground and the other electrode connected through a resistor to a suitable power supply 18 illustrated as a battery. A condenser 22 is connected across the two electrodes 'of the'neon tube 21. The ungrounded electrode of the neon ltube 21 is connected through an isolating resistor 23 to a reactance tube circuit 12.

The reactance tube circuit 12 is comprised of a triode vacuum tube 25 having a plate electrode 28, a grid electrode 27 and a cathode electrode 26. The plate electrode 28 is connected through an impedance 35 to the power supply 18. The output of the sawtooth generator 11 is connected through the resistor 23 to the grid electrode 27, while the cathode electrode 26 is connected through a parallel combination of resistor 33 and condenser 32 to ground. A resistor 29 and blocking condenser 34 are connected in series between the plate electrode 28 and the grid electrode 27 of the tube 25. A parallel combination of a resistor and a condenser 31 are connected from the grid electrode 27 of the tube 25 to ground. l

A conventional oscillator circuit 13 comprising a triode vacuum tube 37 having a plate electrode 38, a grid electrode 39 and a cathode 40 is connected to the re- 2,727,139 Patented Dec. 13, 1955 f. lCC

actance tube circuit 12. A tuned circuit comprising condenser 42 and inductor 41 in parallel is connected between the grid electrode 39 and ground. A grid leak resistor 43 and a condenser 45 connected in parallel connect the tuned circuit comprising inductor 41 and capacitance 42 to the grid electrode 39. The cathode is connected to the tap 44 0f the inductor 41, while the plate electrode 38 is connected to the power supply 18. The plate electrode 28 of the reactance tube 25 is connected to the tuned circuit comprising the inductance 41 and the capacitance 42 by means of a blocking condenser 36. The ungrounded terminal of the tuned circuit comprising the inductance 41 and capacitance 42 is connected through a resistor 46 to a band pass filter 14.

The filter 14 comprises a condenser 47 connected in series with the combination of a condenser 48 and an inductor 49 in parallel between the resistor 46 and ground.

The output of the band pass filter 14 taken at a point between the condenser 47 and the parallel connected condenser 48 and inductor 49 is connected through a coupling condenser 50 to a reactance tube filter shifter 15. The reactance tube lter shifter 15 is of similar design to the reactance tube circuit 12. The reactance tube lter shifter 15 comprises a triode vacuum tube 54 having a plate electrode 51, a grid electrode 52 and a cathode electrode 53. The cathode 53 is connected to ground through a parallel combination of resistor 61 and a condenser 60. The plate electrode 51 is connected through a resistor 62 to the power supply 18. A series combination of a condenser 55 and a resistor 56 is connected between the plate electrode 51 and the grid electrode 52, while a parallel combination of a resistor 57 and a condenser 58 is connected between the grid electrode 52 and ground. A control voltage from any suitable source for the reactance tube iilter shifter 15 may be connected to the terminal 59. A detector circuit 16 comprising a diode vacuum tube is connected across the plate and cathode circuits of the reactance tube 54. A coupling condenser 63 connects the plate electrode 51 of the tube 54 to the cathode 66 of the diode rectifier 65. The cathode 66 of the diode 65 is connected through an inductor 68 to ground. The plate electrode 67 of the diode 65 is connected to ground through a condenser 69, and a series combination of resistors 70 and 71 connected in parallel with respect to the condenser 69. The common terminal of the resistors 70 and 71 is connected through a variable resistor 73 to the power supply 18.

The plate electrode 67 of the diode 65 is also connected by means of a conductor 72 to a switching means 17. The switching means 17 comprises a triode vacuum tube 76 having a plate electrode 77, a grid electrode 78 and a cathode 79. The conductor 72 is connected to the grid electrode 78, while the plate electrode 77 is connected through a relay coil 80 to the power supply 18. The cathode 79 is connected to ground. The relay 81 comprises a coil 80, contacts 83 and closing bar 84. The relay 81 in the closed position will supply the plate voltage to the intermediate frequency amplifier 5 by conductor 82 from the power supply 18. I t is obvious that a control voltage may be supplied to any stage or stages and to any control element by relay 81.

In the operation of the circuit, an incoming signal, from any suitable source, is fed into the mixer 19 by means of the antenna 3 and radio frequency amplifier' 4. The mixer 19 combines the incoming signal with the signal from the local oscillator 13. The signal from the local oscillator 13 differs in frequency from that of the incoming signal by a specified amount, namely the intermediate frequency. The output of the mixer 19 is fed to the intermediate frequency amplifier 5.

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The frequency range of the incoming signal is scanned or scarchedfby the describedsystem by means ofswee'ping" the local oscillator 13 over-a selected range of frequencies below the range of frequencies ofthe incoming sig; nal; The sweepingaction'ofthelocaloscillatorflk is accomplished by' the sawtooth generator 1 1"an `dftl'1e` reacta/nceftube circuit 1 2.

If a.' certain frequency interval withinthe rargcof'thfe incoming signalis yundesired in the output of the` described system, my invention'allows the'rejec'tion yof this undesired frequency interval. My inyention permits a control sys'- terntliat is absoluteinact'ion and the frequelCYf interval of rejection is held constant rga'rdle'ssofthe, leyelqf the incoming'sgnal.

' The lter 14 is a frequency sensitive'network of simple and in Xpcnsiye design.' Its actioni ist'ofA pass"r, rej'ec't frequenciesV between certain fregluexilV limits. In my specificY example; 1 utilize a"ba `ndpass type filter. This ne orlt may bea relatively sirn'plefilter such, as one madeof inductance 49 andjcapa'cit'an'c'es 47 and 48. The

response curve of atypical filter is`shoWn in Fig. 2 where 1 have plottedthe outputvoltage of rectifier 1 6"versus frequency. The filte r 14,is peaked or tuned ltof the ,center of a` frequency interval of .theloal oscillator`13 differing fromA the'fundesied frequency interval of theincoming signal'by an amount equalto vthe intermediate, frequency,

' The` center frequency 90f ofthe filtefr 14 may beshifted automatically over a small range of frequencies ,near the original; center frequencyif'desired. Thisniay be accomplishedfby the recta'nceltube filter. shifterv 15.- 'Ifhe'a'ppli-V cationfofa voltage on the terminal59- fromfan indeperid ent s'iire'to the frequency shifter 15 will'sliift the center frequency of the filter 14 as desired.

The output ofthe filter'14l is fed into therectilen or orcircuit 16 in orderto'prvide a, diretfc'urrenf whosef magnitude is. dependent on, thev4 response" of" the flter"1i4j. A1 bias voltage is suppliedfto'thefrectifer'cir f 1ffrorn the fpover supply 18' throughftlie variable r' 1s n ce y7 3 a d is .ac 1d.=, cl',to thelouy o ftll'ferec'tifier 1 6:h t'of set ordete'rmi'ne th'e'rfrequenc'y terval Width Q91 The center frequency.' 90V1 remains constant and the. Width of. th fre'guerieyV interval 91 may be' varied bymerely)- rig the@ variable resistor'73,` which raises .or lowers the'res'pons'e' curve in' Fig. v2. The-output' voltagederived from t V ef detector-f16-and' the ,bias voltageis o f sufficient magnitudeto .operate the'switching stage Y1A7. The ,V''lt a"g' `e` Y I clalni as my iriventio 1. 1n ajr'adio" apparatus; generiertena rsf'reaefane tube circuit driven by said generator, an oscillator having" a'l tunedcircuit; means connecting 's'aid :reactancetube circuit across the tuned circuit of said oscillator, a tuned filter circuit connected across the output of said oscil- 5 lator, a second reactance tube circuit connected to said filter circuit for varyingAthe-tun ing of said filter circuit, a detector connected acrossthe output of said filtercircuit for rectifyin'g" theY potential?apnearirigfacross.` saidL lter circuit, a variable .bias lcontrol connected to said detector circuit s v vitching means ,and meansfconnecting theo 1,1 t1,x u t of t SadidfectQY-- tO Sii ithi's l'sn. 'for dSfnSifi'z-is said Aapiaratus FWithin a predeterminedgfrequeneyinterval.

2. A frequency selective control system fo r' 'rad i o apparatus comprising a f localoscillator',y ai frequency sensitive circuit, a reactanceutuneVA circuitv connected to said frequency sensitivek circuit for'varying the frequency of sensitivity of said frequency sensitive circuit, a rectifier circuitconnected totheoutput 5o f saidzfrequency, sensitive lcoupliii the'foutnutlof-said rectifierE atiis .:for'.A de sensiti z 1 ng5 said radio 'anpara'tus rWithin afpfrdetermined. frequency interval..v

`3n Radin` apnaratus, comprising a mixer circuitfhaying; ntlforfinco Afrequencysignals, aglocal oscillator' controlledy byu a s'xlv'eepY generator adapted-:for-- scann`ng over. @selected,range of frequencies below that frange-f,offfrequeneiesfover which the incoming ofi-th signalsare anticipated?V said..,loca1 oscillatorand incoming f yonn'ctedfto'said'mixercircui a. control 'includmgga filter,F connected to saidlocal oscilla-A t'or",4 areetifyingmeans connected to the output ofsaidy fil. te r,. av filter.shifterC connected to said filter and-. contrillled, byi 'an' indette* aepgvariabie, a switching.. cirluit dltoltlie output o fQsaid rectifier for altering-*the vity of ls'id. radio. apbaratusl Within" a;v 'predeterj rriined.. vf requency interval determined bysaid filter.V

4.l In-con1bination radioapparatuscomprising' a local oscillator, means for controlling saidllocalf oscillatorV by a sweep' generator, adapted ,fon scanning" over :a selectedI rarige'of frequencies below a range of, frequencies: over which the incon 1ing signals are: anticipated; a' control circuit comprising alte'r connectedftdtle output of said localoscillator,V rectifyingnieans connected to'4 the output ofsaid' flter, means .for adding .astealdy directbias voltage to said. rectifier. to. determine a selected range o fffrequencies`-. overv v'vhicliV theQrecti'fierA operates; and rneans'- for .applying theoutput frornsaid'frectifer tol alten the sensitiyity, of saidrradio, apparatus to said-tir.1 coming signals within a. pre/determined. frequencylin? terval.

5. frequency sensitive circuit Whichisf non. respon sii/'c oyer a predetermined v. frequencyfinterval, Within a. frequency band comprising. in combination -a -,local oscil ltr a t. *t

vvliicl'ftheincoming'signal 1s anticipated, a freq-uen oy tive .control circuit-,including afilter vconnectedto thevoutfilter Ato,l alter-,the-y sensitivity"` of` said' circuit' within ay predetermined'-.frequencyA interval 5.-` in'fonibinaiion; radiof app'aramsvcomprising a mixer circuit; aninterrnedia'te frequency amplifying means, a locali oscillator controlled vby a: sweep' generator adanted meegeven@ to. whihfa @metSantana-mwa putfofj saidlocal-oscillator, a frectifying; meansV connectedl the output of said local oscillator, a rectifying means connected to the output of said lter, a steady-*direct bias voltage added to said rectier output to determine the range of frequencies over which the output from said rectifier is utilized, a switching circuit, means for connecting the output of said rectifier to said switching circuit, said switching circuit having its output coupled to a stage of said radio apparatus to alter the sensitivity of said radio apparatus to said incoming signals within a predetermined frequency interval.

References Cited in the le of this patent UNITED STATES PATENTS Poeh June 18, Usselman Nov. 30, Boothroyd Nov. 1, Andrews Feb. 13, Heller Aug. 26, Guyton Sept. 22, Herman Feb. 9, 

